Process for heating industrial furnaces

ABSTRACT

The invention relates to a process and apparatus for heating industrial furnaces wherein liquid fuel oil at a temperature of 250*C. to 500*C. and a pressure of 8 to 50 bars is mixed with a quantity of primary air amounting to 25 to 60 percent of the amount required for complete combustion, and this mixture is subsequently mixed with a quantity of secondary air amounting to 15 to 35 percent of the amount required for complete combustion.

United States Patent [1 1 Hicguet 1 PROCESS FOR HEATING INDUSTRIAL FURNACES [75] Inventor: Max Hicguet, Boulogne-Billancourt.

France 73 Assignee: Societe DEtudes Et De Recherches Schentifiques Et Minieres, Seine Saint-Denis, France [22 Filed: Dec.2l, 1972 211 Appl. No.: 317,121

[30] Foreign Application Priority Data Dec. 23, 1971 France 71.46373 [52] US. Cl 432/19, 266/29, 432/96, 432/101 [51] Int. Cl. F271) 1/10 [58] Field of Search 4.32/19 20, 24, 96, 101; p v, V 266/29 [56] References Cited 7 I UNITED STATES PATENTS 5/1963 Smith 432/ June 11, 1974 3,400,921 9/1968 Hemker 266/29 3,582,053 6/1971 Limp ach 432/101 X Primary Examiner..lohn J. Camby Attorney, Agent, or Firm-Stevens, Davis, Miller & Mosher [57 ABSTRACT The invention relates to a process and apparatus for heating industrial furnaces wherein liquid fuel oil at a temperature of 250C. to 500C. and a pressure of 8 to bars is mixed with a quantity of primary air amounting to 25 to percent of the amount required for complete combustion, and this mixture is subsequently mixed with a quantity of secondary air amounting to 15 to 35 percent of the amount required for complete combustion.

8 Claims, 9 Drawing Figures PATENTEDJun 1 1 1914 SHEEIIDF 5 PATENTEDJUM 1 m4 SHEET 2 OF 5 PATENTED Jul 1 1 sum sor 5 PROCESS FOR HEATING INDUSTRIAL FURNACES The present invention relates to the heating of industrial furnaces.

In US. Pat. No. 3,625,497 there is described a process for roasting in a vertical furnace. In that process a mixture of air and dry vapors of fuel oil at a temperature of 300 to 400C, in the form of a mixture with an amount of air less than 40 percent of that required for the complete combustion of the fuel oil present, is introduced into the furnace in order to burn there.

In order to produce such a mixture, it has been proposed to heat the fuel oil to a temperature of the order of 300 to 350C. under a'pressure of the order of bars, then to expand it to atmospheric pressure or to a pressure slightly above atmospheric pressure for example about 0.5 bar so as to produce vapor, to heat this vapor, and finally to add hot air to the vapor before, during or after the heating of the vapor. The mixture is thereafter fed to the furnace.

The object of the present invention is especially to make the production of fuel oil vapors, for feeding furnaces, easier and more economical.

According to a first aspect of the present invention there is provided a process for the heating 'of industrial furnaces by means of vapors produced by expansion of hot liquid fuel oil under pressure, the process comprising taking a starting material consisting of liquid fuel oil at a temperature of 250C. to 500C, under a pressure of the order of 8 to 50 bars, injecting the fuel oil into a pre-combustion and heating chamber in free communication with the interior of a furnace in such a manner that it expands and vaporizes in said chamber, introducing primary air into this same chamber in the immediate vicinity of the fuel inlet, introducing secondary air at a distance from the fuel. inlet, and'introducing the resulting mixture into the interior of the furnace, the rate of introduction of air in each case relative to the amount of air required for completecombustion of the fuel oil being 25 to 60 percent in the case of the primary air and to 35 percent in the case of the secondary air.

The primary air introduced in the vicinity of the fuel inlet causes partial combustion of the fuel, with conver-v sion of a large part of the carbon contained in the fuel oil into carbon monoxide, and the secondary air causes the practically complete conversion 'of the remainder of this carbon into carbon monoxide while moderating the temperature of the walls of the chamber for precombustion and heating of the fuel vapors, in particular near the burner or burners through which the fuel oil is injected. A further charging of secondary air introduced may be fed in at a later stage in the combustion cycle.

The production of fuel oil vapor from hot liquid under pressure differs from the known mechanical spraying or atomizing, in which a liquid fuel which is cold or at a slightly elevated temperature is converted into small droplets which thereafter vaporize more or less imperfectly to producea carbonaceous deposit.

The pressure range of about 8 to 50 bars is so chosen that regardless of the viscosity of the fuel oil (whether it is light fuel oil or heavy fuel oil), the fuel oil remains liquid at the temperature employed.

The air can be introduced hot throughout, preferably at a temperature of at least 250C. or can only be introduced hot during the light up phase of the boiler operating cycle and thereafter be replaced by cold air. It is furthermore possible, according to the present invention to introduce as hot air, both the primary air in the vicinity of the fuel inlet and secondary air at a distance from this inlet.

The term industrial furnaces is used throughout the description and claims to denote both furnaces such as furnaces for roasting chalk, dolomite or magnesia, and blast furnaces and boilers.

In the case of blast furnaces, air at a very high temperature, generally of the order of 800C. to l,350C. is available; this can be used as it is, if necessary introducing cold a small portion of the primary air, so as to moderate the temperature of the walls of the fuel oil injection nozzles.

According to a second aspect of the present invention there is provided apparatus for carrying out the above process such apparatus comprising a space into which the fuel oil is to be injected, and a nozzle which comprises a central device terminating in a calibrated outlet orifice for introducing the fuel into said space,

and a peripheral device for introducing primary air in the immediate vicinity of the calibrated orifice.

The device for introducing the fuel may comprise a hollow blowpipe which is detachable so as to be interchangeable with other similar blowpipes, and has an intemal chamber which opens into a calibrated orifice or jet which regulates the flow rate of the fuel, and at the outlet of which orifice the fuel expands.

The description which follows in relation to the attached drawing and given by way of a non-limiting example, will make it possible easily to understand how the invention can be carried out.

FIG. 1 is a transverse section of a vertical furnace equipped for carrying out the method of the invention;

FIG. 2 represents a detail on a larger scale;

FIG. 3 relates to a variant of FIG. 2 and FIG. 4 to a variant of a part of FIG. 1;

FIG. 5 is a schematic vertical section of a blast furnace equipped for carrying out the method of the invention;

FIG. 6 is a section along VI-VI of FIG. 5.

FIG. 7 shows schematically on a large scale a detail of the fuel oil nozzleof FIG. 5;

FIG. 8, similar to FIG. 7, relates to an alternative embodiment of a fuel oil nozzle; and

FIG. 9 is similar to FIG. 1 and shows schematically an installation for heating and for distributing the fuel between the various nozzles.

FIGS. 1 and 2 show a vertical furnace such as is used, for example, for roasting dolomite. The furnace comprises an internal tubular portion made of bricks 1, consisting of a basic material such as magnesia or dolomite, an intermediate layer 2 also of basic material, and an external layer 3 which is heat insulating and made of acid bricks, the whole beingencased in a sheet metal jacket 4.

- Radially extending pre-combustion and heating chambers 9 for the fuel vapors are defined in the wall of the furnace byplanes which are themselves radial to the axis of this furnace. In the example they number eight, but there can be fewer for example four, or more for example 12 or more, depending on the diameter of the furnace.

A nozzle 11, shown in more detail in FIG. 2, enters each chamber 9 from the outside. The nozzle 11 comprises a blowpipe consisting of an axial tube 11a which at its outward end carries ajet consisting of a plug 11b in which a calibrated outlet orifice He is machined; in turn, the blowpipe is placed in a tube 11d serving as a jacket; the annular space 11f between the jacket 11d and a tube 11:: of greater diameter serves to introduce primary air, which is preferably caused to rotate.

The liquid fuel is fed in hot (250C. to 500C.) and under pressure (8 to 50 bars) through the tube 1 la and is ejected through the orifice 110. The primary air, preferably at a temperature of at least 250 C., is introduced through the space 11f contained between the jacket 11d and the tube llle so as to issue in the immediate vicinity of the point of injection of the fuel. The entire nozzle 11 can be carried by a fitting 11g attached to the walls of the antechamber 9.

The fuel oil vapor produced at the outlet of the tube 1 la burns partially or completely in the chamber 9 and issues from the latter at its inner end, while entering the internal space of the furnace.

The blowpipe 11a, 11b is preferably detachable so that it can be cleaned, or if necessary replaced by another the plug of which has a calibrated orifice of different diameter so as to change the fuel flow rate or be appropriate for a fuel having a different viscosity.

In the example of FIGS. 1 and 2 it has been assumed that behind the air vents, that is to say behind the orifices of the antechamber 9, the furnace-had a. greater diameter, as is indicated at 12, so that at the bottom of an air vent there is no shelf on which material moving down the furnace could rest.

In the embodiment of FIG. 3 the nozzle consists principally of a central tube 150 which carries internally at its end a plug15b having a calibrated orifice 15c, and which is mounted in a tube 15d of greater diameter. The fuel oil is introduced through the tube 150 and the primary air is introduced through the annular space 15e between the two tubes.

In the embodiment of FIG. 4, the chamber 16 instead of being in the shape of a truncated pyramid as in FIG. 1 opens into the inner space of the furnace through an air vent of restricted cross-section machined in the innerrow of bricks. The side walls 17a and 17b of the antechamber and those 18a and 18b of the air vent are connected to one another by incurved walls 19a and 1% which thus form a zone of turbulence for the fuel oil vapors and for the primary air coming from the nozzle 20.

The blast furnace represented schematically in FIGS. 5 and 6 is provided, in its so-called working portion,

by a multiplicity of radiating blow nozzles 21 connected by couplings 23 to a toroidal manifold 22 fed with hot air from the customary recuperator (not shown).

A fuel nozzle 24, shown in detail in FIG. 7, is mounted in each blow nozzle. For the introduction of fuel oil the burner comprises an internal tube 24a which carries at its end a plug 24b having a calibrated orifice 240. For the introduction of 'cold or hot primary air the nozzle 24 has an annular chamber 24d defined by an internal tube 25e and an external tube 25f. The fuel nozzle 24 is held in an axial position within the blow nozzle 21 by means of a fitting 26.

In an alternative embodiment shown in FIG. 8 the nozzle 24, instead of being mounted axially in the blowpipe 21, is mounted obliquely relative thereto with its axis in a plane which passes through the axis of the blow nozzle and which is either vertical as shown, or if necessary is inclined horizontal.

The plugs or jets such as 11b, 15b and 24b can be produced in a known manner so as to impart a vortical movement to the issuing liquid fuel.

In the installation shown in FIG. 9, the furnace equipment is similar to that of FIG. 1 and all that will be described here is that which concerns feeding the nozzles 27 with a liquid fuel from a tank 28.

The tank 28, or the pipeline 29 connected thereto. is equipped with a heating device 30. The pipeline 29 is connected to a toroidal manifold 31 and includes a pump 32. Inorder that the temperature of the fuel in the pipeline 29 shall be raised, preferably gradually, to the desired value, at least one heating device is combined with this pipeline. Three such heating devices have been shown in the drawing, the first 33 being in the form of a heating resistance, the second 34 being in the form of a coil forming part of a circuit passing a source 35 of hot fluid (gas or vapors, fumes or thermal fluid), and the third 36 being in the form of a resistance which encloses not only the tube 29 but also the manifold 31.

' The diameter of the tube 29 and that of the toroidal manifold 31 are so chosen that the fuel pressure is practically constant and that the various nozzles are fed at comparable flow rates. However, if it is desired to favor one or more of the nozzles, it suffices to provide the latter favored nozzle or nozzles with jets of a higher flow rate. This may be the case if, for example instead of being round, the furnace is of polygonal, such as square, cross-section and if in consequence certain jets are further from the center than are others.

I claim:

1. A process for heating industrial furnaces with vapors produced by expansion of hot liquid fuel oil under pressure, comprising: providing liquid fuel oil at a temperature of 250 to 500C, under a pressure of 8 to 50 bars, injecting said heated and pressurized fuel oil into a precombustion and heating chamber which is in free communication with the interior of a furnace, thereby expanding and vaporizing said fuel oil in said chamber, introducing air into saidchamber in the immediate vicinity of the fuel inlet thereto and introducing the resulting mixture into the interior of the furnace.

2. A process as set forth in claim 1, in which said air is primary air, and secondary air is introduced at a distance from the fluid inlet.

3. A process as set forth in claim 2, in which the rate of introduction of air relative to the amount of air required for complete combustion of the fuel oil is 25 to 60 percent in the case of the primary air and I5 to 35 percent in the case of the secondary air.

4. A process as set forth in claim 3, in which the rate of introduction of primary air represents 35 to 40 percent of the amount required for'complete combustion.

5. A process as set forth in claim 4, in'which the liquid fuel oil is provided at a temperature of 280C to 400C.

6. A process as set forth in claim 1, wherein the air is heated before introduction.

7. A process as set forth in claim 6, wherein the air is heated to at least 250C. before introduction.

8. A process as set forth in claim 6, wherein the air is introduced hot only during the light up phase of the furnace operating cycle. 

1. A process for heating industrial furnaces with vapors produced by expansion of hot liquid fuel oil under pressure, comprising: providing liquid fuel oil at a temperature of 250* to 500*C, under a pressure of 8 to 50 bars, injecting said heated and pressurized fuel oil into a precombustion and heating chamber which is in free communication with the interior of a furnace, thereby expanding and vaporizing said fuel oil in said chamber, introducing air into said chamber in the immediate vicinity of the fuel inlet thereto and introducing the resulting mixture into the interior of the furnace.
 2. A process as set forth in claim 1, in which said air is primary air, and secondary air is introduced at a distance from the fluid inlet.
 3. A process as set forth in claim 2, in which the rate of introduction of air relative to the amount of air required for complete combustion of the fuel oil is 25 to 60 percent in the case of the primary air and 15 to 35 percent in the case of the secondary air.
 4. A process as set forth in claim 3, in which the rate of introduction of primary air represents 35 to 40 percent of the amount required for complete combustion.
 5. A process as set forth in claim 4, in which the liquid fuel oil is provided at a temperature of 280* C to 400*C.
 6. A process as set forth in claim 1, wherein the air is heated before introduction.
 7. A process as set forth in claim 6, wherein the air is heated to at least 250*C. before introduction.
 8. A process as set forth in claim 6, wherein the air is introduced hot only during the light up phase of the furnace operating cycle. 